Nonaqueous electrolyte secondary battery

Abstract

A nonaqueous electrolyte secondary battery is prevented from decreasing the remaining capacity and returned capacity at the time of continuous charge at high voltages and high temperatures. The battery has positive and negative electrodes, and a nonaqueous electrolytic solution containing ethylene carbonate and fluoroethylene carbonate as a solvent. The positive electrode contains a positive-electrode active material with the fine particles of a rare earth element compound deposited on its surface in a dispersed state.

What is claimed is: 
     
       1. A nonaqueous electrolyte secondary battery comprising:
 a positive electrode; 
 a negative electrode; and 
 a nonaqueous electrolytic solution, 
 wherein: 
 the nonaqueous electrolytic solution contains fluoroethylene carbonate as a solvent and the solvent further contains ethylene carbonate; 
 the positive electrode contains a positive-electrode active material with fine particles of an oxyhydroxide or hydroxide of at least one element selected from the group consisting of erbium, praseodymium, neodymium, ytterbium, terbium, dysprosium, holmium, thulium, lutetium, and samarium, deposited on the surface thereof in a dispersed state; and 
 the fine particles of the oxyhydroxide or hydroxide have an average particle size of not more than 100 nm. 
 
     
     
       2. The nonaqueous electrolyte secondary battery of  claim 1 , wherein:
 the volume ratio of the fluoroethylene carbonate (FEC) to the sum of the ethylene carbonate (EC) and the fluoroethylene carbonate (FEC) satisfies the relation of 0.2≦FEC/(EC+FEC). 
 
     
     
       3. The nonaqueous electrolyte secondary battery of  claim 1 , wherein:
 the positive-electrode active material is obtained by a method including a process of precipitating the oxyhydroxide or hydroxide on the surface of the positive-electrode active material dispersed in a solution. 
 
     
     
       4. The nonaqueous electrolyte secondary battery of  claim 1 ,
 wherein the positive-electrode active material is a lithium-containing transition metal composite oxide with the fine particles deposited directly on the surface thereof. 
 
     
     
       5. A nonaqueous electrolyte secondary battery comprising:
 a positive electrode; 
 a negative electrode; and 
 a nonaqueous electrolytic solution, wherein: 
 the nonaqueous electrolytic solution contains fluoroethylene carbonate as a solvent and the solvent further contains ethylene carbonate; 
 the positive electrode contains a positive-electrode active material with fine particles of an oxyhydroxide or hydroxide of at least one element selected from the group consisting of erbium, praseodymium, neodymium, ytterbium, terbium, dysprosium, holmium, thulium, lutetium, and samarium, deposited on the surface of the positive-electrode active material in a dispersed state; and 
 the volume ratio of the fluoroethylene carbonate (FEC) to the sum of the ethylene carbonate (EC) and the fluoroethylene carbonate (FEC) satisfies the relation of 0.2≦FEC/(EC+FEC). 
 
     
     
       6. The nonaqueous electrolyte secondary battery of  claim 5 , wherein:
 the oxyhydroxide or hydroxide is at least one oxyhydroxide or hydroxide selected from the group consisting of erbium, praseodymium, and samarium. 
 
     
     
       7. The nonaqueous electrolyte secondary battery of  claim 5 , wherein:
 the oxyhydroxide or hydroxide is an oxyhydroxide or hydroxide of erbium. 
 
     
     
       8. The nonaqueous electrolyte secondary battery of  claim 5 , wherein:
 a ratio of the ethylene carbonate (EC) and the fluoroethylene carbonate (FEC) to an entire volume of the solvent satisfies the relation of 
 0<(EC+FEC)/the entire volume of the solvent<0.6. 
 
     
     
       9. The nonaqueous electrolyte secondary battery of  claim 5 , wherein:
 a ratio of the ethylene carbonate (EC) and the fluoroethylene carbonate (FEC) to an entire volume of the solvent satisfies the relation of 
 0.2<(EC+FEC)/the entire volume of the solvent<0.5. 
 
     
     
       10. The nonaqueous electrolyte secondary battery of  claim 6 , wherein:
 a ratio of the ethylene carbonate (EC) and the fluoroethylene carbonate (FEC) to an entire volume of the solvent satisfies the relation of 
 0.2<(EC+FEC)/the entire volume of the solvent<0.5. 
 
     
     
       11. The nonaqueous electrolyte secondary battery of  claim 7 , wherein:
 a ratio of the ethylene carbonate (EC) and the fluoroethylene carbonate (FEC) to an entire volume of the solvent satisfies the relation of 
 0.2<(EC+FEC)/the entire volume of the solvent<0.5.